Description of Plastic Compression Molding

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Description of Plastic Compression Molding
(red car image by Istvan Ferge from

Compression moulding is one of the oldest known moulding processes, according to Professor of Composite Materials Engineering at Winona State University, Fariborz Parsee. The practice transforms plastic materials that harden when cooled. Compression moulding creates usable objects out of plastics.


The first compression moulds were handmade. In the 1800s, plastic products like hand-held mirrors were made from handmade compression moulds. Professor Parsee says the first plastic products included buttons, brushes and mirror handles. The manufacturing process, known then as "compression moulding," was suitable for the production of simple, small geometric-shaped items.

Automatic Machines

The first automatic compression machine patent was secured in the 1930s. Soon after, hundreds of them were sold to plastic companies. Alfred Critchlow is said to be the founder of the first plastic moulding company, the Pro Corporation. They produced items like daguerreotype cases and hand-held mirror frames between the years 1856 and 1866. Companies later began using large-scale compression moulding machines. Science gave companies more control over the compression moulding process.


A variety of considerations make compression moulding a failure or success. One such factor is mould heating. Molds must undergo the right heating rate and method to yield the desired results. The mould's compression rate is another important factor, as is compression force. Also, curing time dictates how long an item can sit in a mould before it can be removed. Another essential consideration is the mould's cooling rate. All these variables influence the result of the entire process. Scientific equations help engineers get the balance right.


Plastic compression moulding is a processing technique that forms plastic while simultaneously curing its resin. It requires a lot of external pressure and high temperatures. A curing agent is also obviously necessary. The process initiates when force closes the mould at a constant rate as rapidly as its polymer feed endures compression and heating. When the flow commences, the mould fills. Compression of the melting substance creates the product.


Course notes on polymer processing from Drexel University's Materials Science and Engineering program highlight the typical products the process can produce. The automotive, medical and aerospace industries are three big industries discussed. Items like hood, bumpers and fenders are made in compression moulds. Ultrasound equipment and blood separation machines benefit from the caps and plugs compression moulding machines make. One exciting application of compression moulding includes the production of the electrical connectors guided missiles need.

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